Note 2 - Securities - Available-for-sale Securities (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Securities available for sale, amortized cost	$ 559,938,000	$ 380,403,000
Securities available for sale, gross unrealized gains	5,582,000	7,843,000
Securities available for sale, gross unrealized losses	(5,956,000)	(899,000)
Securities available for sale, fair value	559,564,000	387,347,000
US Government Agencies Debt Securities [Member]
Securities available for sale, amortized cost	368,990,000	242,522,000
Securities available for sale, gross unrealized gains	350,000	516,000
Securities available for sale, gross unrealized losses	(4,954,000)	(897,000)
Securities available for sale, fair value	364,386,000	242,141,000
Collateralized Mortgage Backed Securities [Member]
Securities available for sale, amortized cost	39,299,000	23,869,000
Securities available for sale, gross unrealized gains	698,000	1,021,000
Securities available for sale, gross unrealized losses	(544,000)	0
Securities available for sale, fair value	39,453,000	24,890,000
Municipal General Obligation Bonds [Member]
Securities available for sale, amortized cost	130,681,000	101,991,000
Securities available for sale, gross unrealized gains	4,207,000	5,833,000
Securities available for sale, gross unrealized losses	(278,000)	0
Securities available for sale, fair value	134,610,000	107,824,000
Municipal Revenue Bonds [Member]
Securities available for sale, amortized cost	20,468,000	11,521,000
Securities available for sale, gross unrealized gains	327,000	473,000
Securities available for sale, gross unrealized losses	(180,000)	(2,000)
Securities available for sale, fair value	20,615,000	11,992,000
Other Debt and Equity Securities [Member]
Securities available for sale, amortized cost	500,000	500,000
Securities available for sale, gross unrealized gains	0	0
Securities available for sale, gross unrealized losses	0	0
Securities available for sale, fair value	$ 500,000	$ 500,000